This application claims the priorities of Japanese Patent Application No. 2000-158560 filed on May 29, 2000 and Japanese Patent Application No. 2000-166238 filed on Jun. 2, 2000, which are incorporated herein by reference.
The present invention relates to a probe opening forming apparatus and a near-field optical microscope using the probe opening forming apparatus, and more particularly to an improvement of a method of controlling the size of an opening of a probe.
In general, a microscope can observe a very fine portion without destruction in a non-contact with a sample and can further analyze a component of an observation object as well as a shape and a structure thereof by connecting a spectrum analyzer or the like, and has been applied to various fields.
However, a general optical microscope cannot observe a smaller thing than a wavelength of a light and has a resolution thereof limited.
On the other hand, in an electron microscope, the resolution can be enhanced greatly but it is very hard to carry out an operation in the air or in a solution. Thus, a high resolution microscope such as the electron microscope has not been always satisfactory particularly in the field in which a biological sample is to be treated.
On the other hand, a near-field optical microscope based on a different principle from the general optical microscope or the electron microscope has recently been developed and an application thereof has been expected.
The near-field optical microscope serves to detect a so-called evanescent light.
More specifically, in FIG. 1, a near-field optical microscope 10 has a very small sample 12 to be measured which is put on a flat substrate 14. When an excited light 18 is incident from a light source 16 at such an angle that total reflection is carried out over the back face of the substrate 14, all propagated lights are reflected. However, a surface wave referred to as an evanescent light 20 is generated in the vicinity of the surfaces of the substrate 14 and the sample 12. The surface wave is locally present in a region at a distance within the wavelength of the light around the surface of an object.
A probe 22 having a sharp end is inserted in the field of the evanescent light 20 to scatter the evanescent light 20. A part of a scattered light 21 enters the probe 22 and is guided to a detector 24, and data processing is carried out through a computer 26. Consequently, a distance between the tip portion of the probe 22 and the sample 12 can be grasped.
Accordingly, a stage 30 is moved through the computer 26 and a stage controller 28 and a vertical distance between the tip portion of the probe 22 and the sample 12 is controlled such that the scattered light 21 has a constant intensity, and a surface of the sample 12 which is to be measured is scanned. Consequently, it is possible to accurately grasp the concavo-convex portions of the sample 12 in a non-contact with the sample 12.
In addition, the tip of the probe 22 is only present in the field of the evanescent light 20 and does not come in contact with the object itself to be measured. Therefore, it is possible to observe a thing having a smaller value than the wavelength of the light without destruction in a non-contact with the sample 12.
As shown in FIG. 2, the probe 22 includes a core 32 constituted by a dielectric having a light transmittance and a mask 34 constituted by a metal thin film bonded on the surface of the core 32 through evaporation or the like.
An opening 36 is formed in the tip portion of the mask 34 and a tip portion 32a of the core 32 is appeared from the opening 36.
As a method of forming the opening of the probe, for example, the tip of the core of an optical fiber is sharpened by a selective chemical etching method, a method of heating and stretching the tip or the like.
In vacuum, a metal is heated and evaporated, and is bonded as a thin film to the surface of the sharpened probe, thereby forming a mask of a metal thin film or the like.
Next, the mask of the tip portion is removed through etching method, focused ion beam (FIB) or the like, for example. Consequently, the opening 36 is formed.
The probe 22 thus formed is attached to a head 31 of the near-field optical microscope 10 to carry out the near-field optical measurement described above.
In order to enhance the resolution of the near-field optical microscope, it is necessary to form an opening having a desired size in the tip of the probe with high reproducibility.
However, the mechanical dimension of the opening can be controlled but an optical characteristic such as a light transmittance cannot be controlled during formation by using the opening forming method described above. Consequently, the optical characteristic such as the light transmittance of the opening to which importance should be attached for performance has not been considered.
For this reason, when the fabricated probe is actually attached to the near-field optical microscope to carry out the measurement, the measurement cannot be carried out well in some cases.
Consequently, it has been greatly desirable that a technique for forming an opening having a desired size in the tip of the probe with high reproducibility should be developed in consideration of the optical characteristic such as the light transmittance. However, there has not been a proper technique capable of solving the problem.
In consideration of the above-mentioned problems of the conventional art, it is an object of the present invention to provide a probe opening forming apparatus capable of easily forming an opening having a more desirable size and a near-field optical microscope using the probe opening forming apparatus.
For achieving the above-mentioned object, the probe opening forming apparatus in accordance with the present invention is a probe opening forming apparatus for opening a mask of a tip portion of a probe with a desirable size, comprising a core constituted by a material having a light transmittance and a mask formed on the core and constituted by a material having a ductility and a light shielding property; the probe opening forming apparatus comprising a light source, a light detecting means, a pressing means, a storage means, a calculating means, and a pressing control means.
Here, the light source causes a light to be incident in the probe.
The light detecting means detects a quantity of a light transmitted from the tip portion of the probe through a light of the light source, which is on contact with the tip portion of the probe.
The pressing means presses the tip portion of the probe against the light detecting means in a direction of an optical axis.
The storage means previously stores information about relation of the quantity of the light transmitted from the tip portion of the probe and the size of the opening.
The calculating means obtains the value of the light quantity for obtaining an opening having a desirable size based on the information about the relation of the quantity of the light transmitted from the tip portion of the probe and the size of the opening which is stored in the storage means.
The pressing control means controls the press of the tip portion of the probe against the light detecting means in the direction of the optical axis through the pressing means such that a value of a light quantity detected by the light detecting means is equal to the value of the light quantity calculated from the calculating means.
The core constituted by a material having a light transmittance is formed of an optical fiber material such as quartz, a semiconductor, CaF2, chalcogenide or the like.
Moreover, the mask constituted by a material having a ductility and a light shielding property is formed of a metal thin film to be used for a mirror, for example, gold, aluminum, silver, chromium or titanium which is formed on the core through evaporation or the like.
Furthermore, the mask formed in the tip portion of the probe is opened in the following manner. The mask formed in the tip portion of the probe has a ductility. Therefore, when the tip portion of the probe and the light detecting means are pressed in a direction of an optical axis, the mask is gradually stretched thinly so that an opening is formed. The tip portion of the core is appeared from the opening of the mask.
Moreover, the light quantity value of the light transmitted from the tip portion of the probe is zero when the opening is not formed on the mask. When the opening is formed in the mask, the light quantity value is increased in proportion to the size of the opening.
In the probe opening forming apparatus according to the present invention, a feeding means presses the tip portion of the probe and the light detecting means in the direction of the optical axis is suitably used for the pressing means such that the mask of the tip portion of the probe is gradually stretched thinly and opened without a breakage.
In the probe opening forming apparatus according to the present invention, moreover, it is also suitable that a photodiode excellent in the responsiveness of an output value for a light receiving quantity should be used for the light detecting means.
Here, the photodiode receives a light transmitted from the tip portion of the probe through a light receiving portion and outputs a current value proportional to the quantity of the received light.
Also, for achieving the above-mentioned object, the near-field optical microscope in accordance with the present invention comprising the probe opening forming apparatus in accordance with the present invention, a field of an evanescent light on a surface to be measured in a sample is scattered through a tip portion of a probe having an opening formed thereon by the opening forming apparatus, the scattered light is collected through the opening or the evanescent light leaking out of the opening is irradiated on the surface to be measured, and the scattered light or a reflected light is collected through the opening, thereby obtains information about the surface to be measured in the sample.
Preferably, in the present invention, a feeding means controls a distance between the tip portion of the probe and the surface to be measured in the sample in a direction of an optical axis is used for the pressing means.
Preferably, in the present invention, the near-field optical microscope comprises an opening diameter checking mechanism is an opening diameter checking mechanism for checking a size of an opening in a tip portion of a probe having the opening formed thereon, the opening diameter checking mechanism includes a light source, a light detecting means, a pressing means, a storage means, and a comparing means.
Here, the light source causes a light to be incident in the probe.
The light detecting means detects a quantity of a light transmitted from the tip portion of the probe through a light of the light source, which is on contact with the tip portion of the probe.
The pressing means presses the tip portion of the probe against the light detecting means in a direction of an optical axis.
The storage means previously stores information about relation of the quantity of the light transmitted from the tip portion of the probe and the size of the opening.
The comparing means applies a value of a light quantity detected by the light detecting means to the information about relation of the quantity of the light transmitted from the tip portion of the probe and the size of the opening which is stored in the storage means, thereby obtains the size of the opening in the tip portion of the probe.
Preferably, in the present invention, the near-field optical microscope comprises an opening diameter regulating mechanism for changing a size of an opening in a tip portion of a probe having the opening formed thereon, the opening diameter regulating mechanism includes a light source, a light detecting means, a pressing means, a storage means, a setting means, a calculating means, and a pressing control means.
Here, the light source causes a light to be incident on the probe.
The light detecting means detects a quantity of a light transmitted from the tip portion of the probe through a light of the light source, which is on contact with the tip portion of the probe.
The pressing means presses the tip portion of the probe against the light detecting means in a direction of an optical axis.
The storage means previously stores information about relation of the quantity of the light transmitted from the tip portion of the probe and the size of the opening.
The setting means sets a desirable size of the opening in the tip portion of the probe.
The calculating means obtains the value of the light quantity for obtaining an opening having a size set by the setting means based on the information about the relation of the quantity of the light transmitted from the tip portion of the probe and the size of the opening which is stored in the storage means.
The pressing control means controls the press of the tip portion of the probe against the light detecting means in the direction of the optical axis through the pressing means such that a value of a light quantity detected by the light detecting means is equal to the value of the light quantity calculated from the calculating means.
As described above, according to the probe opening forming apparatus according to the present invention and the near-field optical microscope using the probe opening forming apparatus, pressing control means for controlling the press of a tip portion of a probe with light detecting means in a direction of an optical axis through pressing means such that a value of a light quantity detected by the light detecting means for detecting a quantity of a light transmitted from the tip portion of the probe is equal to a value of a light quantity for obtaining an opening having a desirable size. Therefore, it is possible to easily form an opening having a desirable size in the tip portion of the probe.
According to the near-field optical microscope in accordance with the present invention, moreover, an opening diameter checking mechanism for checking the size of the opening in the probe having the opening formed thereon is provided. Consequently, the size of the opening of the probe can be checked easily.
According to the near-field optical microscope in accordance with the present invention, furthermore, an opening diameter regulating mechanism for changing the size of the opening in the probe having the opening formed thereon is provided. Consequently, the size of the opening of the probe can be changed easily.